FesBRuARY 8, 1884. ] 
THE EVOLUTION OF THE CEPHALO- 
PODA.1—II. 
Tue individual coiled shell of every existing 
Nautilus may be said to pass through the stages 
of the protoconch, when it is always nearly or 
quite straight; then through the first of the 
conch, when it becomes slightly curved; then 
through a more completely curved period, in 
which the first whorl of the spiral is completed. 
After this it continues the spiral, the whorls 
on the outside touching the exterior of the 
inner ones, and spreading so rapidly by growth 
as to begin to envelop them, and, in extreme 
cases, to completely cover them up. 
The natural inference from these facts would 
be, that there was a similar succession of forms 
in past times, —the straight in the most remote, 
the arcuate and the gyroceran in succeeding 
periods, and the nautilian only in compara- 
tively modern times. This would be a per- 
fectly clear and legitimate mental conception. 
The structural relations of the adult shells 
appeared also to demand the same solution, as 
shown by the researches of Quenstedt, Bronn, 
and Barrande, and later of Gaudry.  Bar- 
rande’s researches also demonstrated that this 
idea could not be maintained, and that there 
were no such serial relations in time. but that 
the whole series of forms were present in the 
earliest period, and occurred side by side in 
each paleozoic formation. This great author’s 
conclusions have had a curious effect upon 
paleontologists. It has been hastily assumed 
by some, that the mental conception was more 
perfect than could be realized in nature; by 
others, that the imperfection of the recorded 
succession was an obvious refutation of the 
doctrine of evolution, and all pursuit of a 
solution unworthy of serious attention. 
Statistically, the logical picture coincides 
with the observed succession in time. The 
straight cones predominate in the Silurian and 
earlier periods; while the loosely coiled are 
much less numerous, and the close coiled and 
involute, though present, are extremely rare. 
The loosely coiled and close coiled gain in 
numbezs in the carboniferous, and the involute 
are more numerous than in the Silurian; while, 
in the later times of the Jura, all disappear ex- 
cept the close coiled and the involute, there 
being a decided predominance of involute 
shells. Thus we are able, by reversing the 
record and travelling back to the Silurian, 
again to see, that antecedent to that period, in 
the protozoic, there must have been a time 
when the straight cones or their immediate an- 
' Conciuded from No. 52, 
SCIENCE. 
145 
cestors predominated, to the exclusion of the 
coiled and perhaps even of the arcuate types 
or varieties. 
The involute shells of the earliest geological 
times were therefore probably evolved from 
the straight cones in regular succession ; and 
we may perhaps hope to eventually get the evi- 
dence of this succession in the formations. 
The exact counterpart of our logical picture. 
as Barrande’ has truly stated, does not, how- 
ever, exist in the known geological records of 
later periods. Judged by the common classi- 
fication, by the prevalent ideas about the affin- 
ities of adult structures, and by the modes of 
occurrence of fossils in the geological forma- 
tions, the forms seem to be without law or 
order in their succession. 
But let us imagine, during the paleozoic, a 
different condition of affairs from what is now 
the general rule. Let us suppose such a thing 
possible as the quick evolution of forms and 
structure, and that in these ancient periods, 
near their points of origin, animals found the 
earth comparatively unoccupied, and were not 
only able, but in fact forced, to migrate in 
every direction into different habitats, and to 
make perpetual efforts to readjust their inher- 
ited structures to the new requirements de- 
manded by these comparatively unoccupied 
fields. Food and opportunity would have 
acted, in such localities, as stimulants to new 
efforts for the attainment of more perfect adap- 
tation and for changes of structure useful to 
that end. We can neither imagine the effort 
to change of habitat and habits, without its 
cause, the primary physical stimulant, nor the 
change of structure, except as a result of the 
direct effort to meet the physical requirements 
with corresponding or suitable structures. 
Let us also compare the changes taking 
place during the whole of paleozoic time with 
those known to have occurred in certain iso- 
lated cases in more recent times; such, for 
example, as that of Steinheim, where a single 
species, finding itself in an unoccupied field, 
proceeded with unexampled rapidity to fill its 
requirements by the evolution of new series 
and many species, all differing from each other, 
but all referable, by intermediate varieties, to 
the original form, —%in this example, really a 
single species, the well-known Planorbis aequi- 
umbilicatus. 
1 We regret that space does not permit some account of th 
author’s wonderful book, the Systéme silurien de la Bohéme. 
While opposed to almost every theoretical conclusion and the 
general arrangement of the facts made by him, we have the 
strongest feelings of respect and admiration for his powers of ob- 
servation, the technique of his work and publications, and the 
surpassing unselfishness of his life, spent in the pursuit of what 
he deems to be vital truths (see Science, Nos. 48, 44) 
